Policies are a powerful fine-grain mechanism that allow you to customise
the behaviour of this library according to your needs. There is more information
available in the policy
tutorial and the policy
reference.

Generally speaking unless you find that the default
policy behaviour when encountering 'bad' argument values does not
meet your needs, you should not need to worry about policies.

Policies are a compile-time mechanism that allow you to change error-handling
or calculation precision either program wide, or at the call site.

Although the policy mechanism itself is rather complicated, in practice
it is easy to use, and very flexible.